Patent GB-1413685-A (GB)
Title: Ignition advance apparatus for an internal cumbustion engine
IPC: F02P7/077
Filed: 1972-11-15
Abstract: 1413685 Ignition systems; timing ignition DUCELLIER & CIE 15 Nov 1972 [17 Nov 1971 4 Aug 1972] 52703/72 Heading F1B In a method of automatically controlling the ignition advance of an internal-combustion engine in accordance with engine speed, a comparison is made between a coded number A which varies with the angular difference α between a datum position on the engine flywheel and a variable position on the flywheel and another coded number B which varies with the engine speed and when the coded number A coincides with the coded number B an ignition impulse is obtained which triggers an ignition spark at that time thus establishing a relationship by way of coded numbers A and B between the angular difference α and the engine speed, the relationship being made to correspond to the required ignition advance curve. As shown in the block diagram of Fig. 1 the ignition advance apparatus comprises an angular coding unit 1 which emits impulses which are transcribed into the coded number A, a speedometer generator 5 giving the coded number B and a comparator 3 to the inputs of which the coded numbers A and B are applied, the comparator supplying a control impulse to ignition apparatus 7 when the coded number A coincides with the coded number B. The speedometer generater comprises a clock 8 determining the time T between two successive impulses which it emits, a computer 11  multiplying the impulses supplied by the angular coding unit according to the slope of the required ignition advance curve for a given speed, a counter 15 detecting a number of impulses N emitted by the computer during a period T and converting it into the coded number B, a register 16 retaining the number B in a memory bank for a period T following the period T of the previous cycle, the number B being reduced to a level compatible with the number A by means of a divider 14 and when being compared with the coded number A to trigger the ignition apparatus when the number coincides with the number A. The clock has a high stability oscillator 9 periodically supplying a sequence of impulses to the computer through a frequency divider 10. The apparatus may comprise a correction unit (not shown) for correcting the angular difference α according to the depression in the engine manifold or according to any other parameter by bringing in a coded number C which is a function of the depression or other parameter which number is combined with the coded number A or the coded number B. The correction unit may comprise a signal generator generating signals of a duration T 1  which is a function of the depression or parameter during which impulses from a clock are received, a computer multiplying the impulses coming from the clock, a frequency divider reducing the number of impulses supplied by the computer, a counter totalling the number of impulses emitted by the frequency divider during the period T 1  and transforming them into a coded number C and a register retaining in a memory storage the coded number C for a period Ti after the period Ti of the previous cycle, the coded number C being combined with the coded numbers A and/or B by means of a mixer before application to one of the comparator inputs.